1. Field of the Invention
The present invention relates to fabrication methods of package structures, and more particularly, to a fabrication method of a package structure having a MEMS (Micro Electro Mechanical System) element.
2. Description of Related Art
MEMS (Micro Electro Mechanical System) techniques integrate electrical and mechanical functions into a single element using microfabrication technology. A MEMS element is disposed on a chip and covered by a shield or packaged with an underfill adhesive so as to form a MEMS package structure. FIGS. 1A to 1F are cross-sectional views of conventional fabrication methods of different package structures with a MEMS element.
FIG. 1A shows a package structure disclosed by U.S. Pat. No. 6,809,412. Referring to FIG. 1A, the package structure comprises a substrate 10, a chip 14 disposed on the substrate 10 and having a MEMS element 141, a plurality of bonding wires 11 electrically connecting the substrate 10 and the chip 14, and a lid 12 disposed on the substrate 10 to cover the chip 14, the MEMS element 141 and the bonding wires 11.
FIG. 1B shows a package structure disclosed by U.S. Pat. No. 6,303,986. Referring to FIG. 1B, the package structure comprises a lead frame 10′, a chip 14 disposed on the lead frame 10′ and having a MEMS element 141, a lid 12 disposed on the chip 14 for covering the MEMS element 141, a plurality of bonding wires 11 electrically connecting the lead frame 10′ and the chip 14, and a packaging material 15 covering the lead frame 10′, the bonding wires 11, the lid 12 and the chip 14.
However, the use of the carriers (the substrate 10 of FIG. 1A and the lead frame 10′ of FIG. 1B) increases the thickness of the overall structures and cannot meet the demand for miniaturization. Accordingly, package structures without a carrier are developed, as shown in FIGS. 1C to 1D.
FIG. 1C shows a package structure disclosed by U.S. Pat. No. 7,368,808. Referring to FIG. 1C, the package structure comprises: a chip 14 with electrical connection pads 140; a MEMS element 141 disposed on the chip 14; and a lid 12 disposed to cover the MEMS element 141, wherein a plurality of conductive through holes 120 is formed in the lid 12, and a plurality of contact pads 122 are disposed at the two sides of the conductive through holes 120, such that the contact pads 122 located at the inner sides of the lid 12 are electrically connected to the electrical connection pads 140 of the chip 14, respectively. Further, a plurality of solder balls 16 is formed on the contact pads 122 located at the outer sides of the lid 12 for electrically connecting the chip 14 to another electronic element.
FIG. 1D shows a package structure disclosed by U.S. Pat. No. 6,846,725. Referring to FIG. 1D, the package structure comprises: a chip 14 with electrical connection pads 140; a MEMS element 141 disposed on the chip 14; and a lid 12 disposed to cover the MEMS element 141, wherein a plurality of solder bumps 142 is formed on the electrical connection pads 140, a plurality of conductive through holes 120 is formed in the lid 12 and a plurality of contact pads 122 are disposed at the two sides of the conductive through holes 120, respectively, and the contact pads 122 located at the inner sides of the lid 12 are electrically connected to the solder bumps 142, and the contact pads 122 located at the outer sides of the lid 12 are used for electrically connecting the chip 14 to another electronic element.
The above structures dispense with a carrier and meet the demand for miniaturization. However, forming the conductive through holes 120 in the lid 12 by drilling incurs high costs. In addition, misalignment or unstable connection can easily occur to the contact pads 122 which flank the conductive through holes 120, thus leading to poor electrical connection and further adversely affecting the electrical connection quality between the chip 14 and the external electronic element. Accordingly, a package structure dispensing with conductive through holes is provided, as shown in FIG. 1E.
FIG. 1E shows a package structure disclosed by U.S. Pat. No. 6,828,674. Referring to FIG. 1E, the package structure comprises: a chip 14 with electrical connection pads 140; a MEMS element 141 disposed on the chip 14; a lid 12 with traces 121 at an outer side thereof; a support 13 attached to the chip 14 for supporting the lid 12; a plurality of bonding wires 11 electrically connecting the traces 121 and the electrical connection pads 140; and a packaging material 15 encapsulating the bonding wires 11, the lid 12 and the chip 14, wherein the packaging material 15 has an opening 150 for exposing a portion of the traces 121 such that solder balls 16 are formed on the exposed portion of the traces 121 so as to electrically connect to another electronic device.
However, the above package structure requires a lithography process for forming the traces on the lid, thus incurring high costs. In addition, the solder balls 16 are confined to the vicinity of the lid to thereby cause solder ball bridge, limit the signal input/output density of the package structure and reduction of the trace, add to the difficulty in attaching the package structure to a circuit board. As such, the application field of the package structure is limited. In addition, corresponding to the package structure, a fine pitch circuit board is required, thus increasing the cost. Further, such a package structure cannot achieve an EMI shielding effect.
Therefore, it is imperative to overcome the above drawbacks of the prior art.